1. Field of the Invention
The present invention relates to a semiconductor apparatus and a semiconductor manufacturing method, and in particular, to a semiconductor apparatus including a gate electrode use polysilicon formed in a trench (i.e., a groove) formed on the surface of the semiconductor substrate via a gate insulation layer and a method for manufacturing the semiconductor apparatus. As such a transistor, a trench type power MOSFET (an Insulation gate type electrical field effect transistor) and an IGBT (an insulation gate type bipolar transistor) are exemplified.
2. Discussion of the Background Art
In general, a vertical type MOSFET is used for a power device such as a power MOSFET, etc. The power MOSFET includes a configuration in that a gate electrode made of polysilicon is formed in a trench as a mainstream. Further, together with the power MOSFET, a gate-source interval protection zener diode (a protection element) and an ESD (Electro Static Discharge) countermeasure use gate protection resistance element and so on are sometimes formed in another region of the same semiconductor substrate. These elements are frequently formed on a polysilicon coat, such as an element separation coat, formed overlying the semiconductor substrate. Thus, a process for forming the polysilicon coat is needed in the power MOSFET.
FIG. 13A is a plan view of a conventional power MOSFET, and FIG. 13B is a cross sectional view illustrating the conventional power MOSFET when viewed from a section along with an extension line X-X′drawn in FIG. 13A. As shown, a N-type epitaxial layer 3 is formed by means of epitaxial growth on a surface of an N-type mono-crystal silicon substrate 1. A trench 7 is formed on a N-type epitaxial layer 3. A gate insulation coat 9 is formed on an inner wall of the trench 7.
In the trench 7, a gate electrode use polysilicon 11 is formed via a gate insulation coat 9. A portion of the gate electrode use polysilicon 11 is drawn from the trench 7 onto the epitaxial layer 3, and is used as a gate contact section 11a. The gate electrode use polysilicon drawn to the epitaxial layer 3 is also utilized as a Gate-source interval protection zener diode or an ESD countermeasure use gate protection resistance element.
A P-type body diffusion layer 13 is formed adjacent to the trench 7 on the surface of the N-type epitaxial layer 3. An N-type source diffusion layer 15 is formed adjacent to the trench 7 on the surface of the P-type body diffusion layer 13. A layer interval insulation coat 23 is formed all over the n-type epitaxial layer 3 covering the gate contact section 11a. A source use connection hole 25s is formed on the layer interval insulation coat 23 on the N-type source diffusion layer 15 and reaches the N-type source diffusion layer 15 and the P-type body diffusion layer 13. A gate use connection hole 25g is formed on the layer interval insulation coat 23 on the gate contact section 11a and reaches the gate contact section 11a. A conductive plug 27 is embedded into each of the connection holes 25g and 25a. A source electrode metal coat 29s is formed on the conductive plugs 27 in the source use connection hole 25s and the layer interval insulation coat 23. A gate electrode metal coat 29g is formed on the conductive plug 27 in the gate use connection hole 29g and the layer interval insulation coat 23. Such a MOSFET is discussed in the Japanese Patent Application Laid Open No. 2006-013487 and a registered U.S. Pat. No. 3,497,751.
In the MOSFET of FIG. 13, due to embedding a poly-silicon into a trench 7, a width of the trench cannot be increased and thereby limited to a prescribed level. When embedding the polysilicon into the trench 7, the polysilicon needs a coat thickness more than half of the trench width. Accordingly, a thicker coat needs to be formed. Specifically, when a portion of the polysilicon coat is left on the silicon substrate like the gate contact section 11a of FIG. 13, for example, resolution deteriorates in the following process of a photoengraving due to a step created on the polysilicon. Further, due to a step of the polysilicon as shown in FIG. 13, a residue 53 appears when a metal wiring patterning is executed. Since downsizing and low pricing are demanded in the future, and accordingly, a resistance increases as a result of the downsizing of a diameter of a contact, it is demanded to keep a sufficient contact area. Thus, a cheep process going with a simple flow is expected while suppressing a step as far as possible on the semiconductor substrate surface.
Further, as a manner of embedding a gate electrode used polysilicon in the trench and forming and connecting a contact, the below described manners have been proposed in a power device. For example, as shown in the JP Application Publication No. 2006-135038, a zener diode or a resistance element is formed from a second polysilicon coat, separately formed from a gate electrode use polysilicon on an element separation coat overlying the silicon substrate. Further, the second polysilicon coat is also formed on a gate contact section of the gate electrode.
However, formation of the second polysilicon coat necessarily increases a number of processes. In addition, a step appears due to the second polysilicon coat, and likely causes a metal wiring residue during patterning of a metal wiring after a layer interval coat is formed. Further, when a fining technologynology is innovated and an interval between a trench-gate electrode and a gate contact section is shortened, an uneven thickness appears in the layer interval insulation coat in the vicinity of a step due to the step created by a second polysilicon coat covering a gate contact section. As a result, a contact depth of the trench section varies, and a performance of the transistor varies. Further, in a photo engraving process for forming a contact, a resist coat thickness varies, and the unevenness causes an uneven diameter of a connection hole and contact resistance. Further, a contact hole formed on the gate contact section of the gate electrode use polysilicon embedded in the trench is small so that a contact resistance increases. Due to a need of embedding a polysilicon into a trench, a trench width has its own limit as long as the above-mentioned embedding manner is used. Accordingly, a diameter of a connection hole is limited to a prescribed level. As a result, it is impossible to form a connection hole of a large diameter capable of flowing more amount of current while decreasing a resistance.
Further, as discussed in the Japanese Patent Application publication No. 2003-515915, a gate contact section of a gate electrode use polysilicon is formed on each of a connection trench, formed by extending a gate trench, and a sidewall made of a gate electrode use polysilicon of an terminal end. However, a diameter of a connection hole formed on each of the trench and the sidewall is small, and a contact resistance increases. Further, due to a need of embedding a polysilicon into a trench, a trench width has its own limit as long as the above-mentioned embedding manner is used. Accordingly, a diameter of a connection hole is limited to a prescribed level.
As a result, it is impossible to form the connection hole with a large diameter capable of flowing more amount of current while decreasing a resistance.